<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    
</body>
 <script>
    let arr = [1,2,3,4,5,6,7,8,9]
     //大于3第一个元素
     var value = arr.find(function(item,index){
         return item > 3;
     })
     console.log(value); 
     //小于7第一个元素位置
     var index = arr.findIndex(function(item,index){
         return item < 7;
     })
     console.log(index); 
     //4填充到数组
     arr.fill(4)
     console.log(arr)
 </script>
</html>